New blood test could replace colonoscopy

If you’ve ever had a colonoscopy, you know how uncomfortable it can be, but the dreaded test for colon cancer may soon be replaced by a simple, noninvasive and reliable blood test, according to a study published in the July issue of the Journal of Molecular Diagnostics.

The study, conducted by South Korean researchers from Genomictree Inc. and Yonsei University College of Medicine in Seoul, indicates that the future of colorectal cancer screening may lie in the development of biomarkers for the disease.

The researchers found that by modifying a certain gene, they could accurately detect the difference between blood samples from people with cancer and blood samples from those who did not have cancer.

Experts say the blood test findings are promising, although they are “not quite ready for prime time.”

“Based on the data they presented, it looks really good,” said the journal’s scientific editor, Chhavi Chauhan. “But to turn this into a diagnostic test available to everyone, the research has to be duplicated by others and with more numbers.”

The simple blood test accurately detected cancer 87 percent of the time. For those without cancer, it was accurate approximately 95 percent of the time. And when the researchers used the diagnostic blood test to look at early, stage I cancer, it was correct around 92 percent of the time.

Although the biomarker blood test is still in its early stages, Dr. Eric Esrailian, co-chief of the division of digestive diseases at the David Geffen School of Medicine at the University of California, called the research “very exciting,”

On the other hand, some are concerned about the blood test not being as accurate as a colonoscopy, at least when it comes to the initial screening for cancer. But Dr. H. Gilbert Welch, a professor of medicine at Dartmouth Institute for Health Policy and Clinical Practice, points out that it has not yet been proven that a colonoscopy is more accurate than the lower tech, less invasive blood test.

Welch adds that the reason colonoscopy became the preferred test is because “the basic idea of it was so appealing" since colonoscopy was being used as the follow-up test for the blood stool test; thus, the procedure became the norm. As Welch put it, the attitude was, “Wow if we do this as a follow-up test, maybe we could just do it on everyone.”

Accordingly, researchers have launched an ongoing study to find out how the two different tests compare in terms of the number of lives that could be saved over a period of 10 years, using patients who have tested positive during an initial screening (testing positive on a stool test doesn’t necessarily mean you have colon cancer, although it does mean you’re risk of getting it is much higher).

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Most people know that screening and early detection for cancer saves lives. Despite that knowledge, however, many people do not get screened – even though screenings have been estimated to lower the risk of dying from cancer by up to 50 percent.

Following lung cancer, colon cancer remains the second leading cause of cancer deaths among both women and men in the United States. According to the Centers for Disease Control and Prevention (CDC), nearly 137,000 Americans were diagnosed with colon cancer in 2009 – and around 40 percent of them will die from it. The American Cancer Society estimates an approximate 142,000 new cases of colorectal cancer will be diagnosed this year in the U.S., and more than 50,000 will die from the disease.

However, there is some positive news among the dire statistics. According to Welch, colorectal cancer has declined 39 percent since 1975.

Meanwhile, invasive colonoscopy is still considered the “gold standard” for early detection of cancer. While stool blood tests are also used, the researchers from South Korea say this newest blood test looks at the "methylation" of genes, which is a biochemical process that is fundamental in how genes are expressed and function.

The researchers tested the gene-based screen in tissues taken from 133 colon cancer patients and, as anticipated, tissues taken from these cancerous tumors showed the characteristic gene changes – and samples taken from adjacent healthy tissues did not.

Significantly, the same genetic marks of colon cancer (or the absence of it), could "be measured in [blood] samples from colorectal cancer patients and healthy individuals,” say the researchers.

Nevertheless, some experts remain cautious about the potential value of this newest blood test.

"Given the overall low rate of adherence to colorectal cancer screening, having other non-invasive options to get everyone screened for colorectal cancer is never a bad thing," said Dr. Bethany Devito, a gastroenterologist at North Shore University Hospital in Manhasset, N.Y.

Devito pointed out though that more research is needed before the blood test becomes fully accepted for use because, unlike similar gene-based stool sample tests, the new test "has not been studied to prove detection of precancerous polyps.”

She added that additional studies with larger sample sizes are needed “to validate its role as an effective screening tool for the detection of not only early colorectal cancer but also precancerous polyps."

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